[x265] Motion.cpp PATCH Analysis summary

[Tom Vaughan]

Hi Vijay.  This sounds great.  Thanks for your contribution.



I think Min Chen was just pointing out that your patch needs to make sure
the number of bmvs doesn’t overflow.



We could hard-code the number of bmvs to keep, but we could also make this
a variable that can be user configurable.



You mention that keeping more bmvs is compute-expensive.  That’s the
challenge with every improvement we try to make.  There is almost always a
tradeoff between improved efficiency and compute cost (speed).  For each
patch, it would be helpful if you would share test results that show the
improvement in efficiency, and the cost in performance.  Some improvements
may only be suitable for very slow performance presets, and we would want
to keep them turned off for fast presets.



You mention that this patch provides better coding efficiency, but you also
say that BD-PSNR and BD-SSIM is same/slightly better, but no degradation.
What is the effect on visual quality?  We care much more about subjective
visual quality than objective quality metrics.  So any subjective quality
analysis is also welcomed.  Any patch that affects outputs will be
evaluated for the effect on subjective visual quality before we commit it.



Tom



*From:* x265-devel [mailto:x265-devel-bounces at videolan.org] *On Behalf Of *N
Vijay Anand
*Sent:* Thursday, August 4, 2016 12:07 AM
*To:* x265-devel at videolan.org
*Subject:* [x265] Motion.cpp PATCH Analysis summary



1. Use of 4 best motion vectors helps in improving

    final bmv about 25% times in simulation.

    i.e 25% times there is a lesser bcost, bmv found

    than with 1 best motion vector.

    This provides better coding efficiency, and for

     100 frames HD seq. (jogging_girl) statistics

    changes from 1-I frame, 46 - Pframe, 53-BFrame

    to 1 I-frame, 45-Pframe, 54 -B frame.



2. 4 is ideal, as more is compute expensive.

    This is number can be hardcoded as a const.

3. BD-PSNR BD-SSIM is same/slightly better with this

    improvements.    But no degradation.





-- 

Principal Architect and Director,

TriSpace Technologies Pvt Ltd.,
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